The present invention pertains generally to bacterial pathogens. In particular, the invention relates to antibodies that elicit functional activity against Neisseria meningitidis serogroup B and also lack autoimmune activity, methods of obtaining and using the same, as well as molecular mimetics identified using the antibodies.
Neisseria meningitidis is a causative agent of bacterial meningitis and sepsis. Meningococci are divided into serological groups based on the immunological characteristics of capsular and cell wall antigens. Currently recognized serogroups include A, B, C, D, W-135, X, Y, Z and 29E. The polysaccharides responsible for the serogroup specificity have been purified from several of these groups, including A, B, C, D, W-135 and Y.
N. meningitidis serogroup B (xe2x80x9cMenBxe2x80x9d) accounts for approximately 50 percent of bacterial meningitis in infants and children residing in the U.S. and Europe. The organism also causes fatal sepsis in young adults. In adolescents, experimental MenB vaccines consisting of outer membrane protein (OMP) vesicles have been found to be approximately 50% protective. However, no protection has been observed in vaccinated infants and children, the age groups at greatest risk of disease. Additionally, OMP vaccines are serotype- and subtype-specific, and the dominant MenB strains are subject to both geographic and temporal variation, limiting the usefulness of such vaccines.
Effective capsular polysaccharide-based vaccines have been developed against meningococcal disease caused by serogroups A, C, Y and W135. However, similar attempts to develop a MenB polysaccharide vaccine have failed due to the poor immunogenicity of the capsular MenB polysaccharide (termed xe2x80x9cMenB PSxe2x80x9d herein). MenB PS is a homopolymer of (N-acetyl (xcex12xe2x86x928) neuraminic acid. Escherichia coli K1 has the identical capsular polysaccharide. Antibodies elicited by MenB PS cross-react with host polysialic acid (PSA). PSA is abundantly expressed in fetal and newborn tissue, especially on neural cell adhesion molecules (xe2x80x9cNCAMsxe2x80x9d) found in brain tissue. PSA is also found to a lesser extent in adult tissues including in kidney, heart and the olfactory nerve. Thus, most anti-MenB PS antibodies are also autoantibodies. Such antibodies therefore have the potential to adversely affect fetal development, or to lead to autoimmune disease.
MenB PS derivatives have been prepared in an attempt to circumvent the poor immunogenicity of MenB PS. For example, C3-C8 N-acyl-substituted MenB PS derivatives have been described. See, EP Publication No. 504,202 B, to Jennings et al. Similarly, U.S. Pat. No. 4,727,136 to Jennings et al. describes an N-propionylated MenB PS molecule, termed xe2x80x9cNPr-MenB PSxe2x80x9d herein. Mice immunized with NPr-MenB PS glycoconjugates were reported to elicit high titers of IgG antibodies. Jennings et al. (1986) J. Immunol. 137:1708. In rabbits, two distinct populations of antibodies, purportedly associated with two different epitopes, one shared by native MenB PS and one unshared, were produced using the derivative. Bactericidal activity was found in the antibody population that did not cross react with MenB PS. Jennings et al. (1987) J. Exp. Med. 165:1207. The identity of the bacterial surface epitope(s) reacting with the protective antibodies elicited by this conjugate remains unknown.
Peptides can serve as mimics of polysaccharides by binding to polysaccharide-specific antibodies as well as to other polysaccharide binding proteins. For example, concanavalin A (Con A), which binds to oligosaccharides bearing terminal alpha-linked mannose or glucose residues, has been used to select peptide mimetics from random libraries of bacterial phage bearing short peptide sequences at the amino-terminus of the pIII coat protein. Oldenberg et al. (1992) Proc. Natl. Acad. Sci. USA 89:5393; Scott et al. (1992) Proc. Natl. Acad. Sci. USA 89:5398. Similarly, monoclonal antibodies have identified peptide mimetics of a carbohydrate present on the surface of adenocarcinoma cells from a phage library. Hoess et al. (1993) Gene 128:43.
Peptides can also elicit polysaccharide-specific antibodies. For example, Westerink et al. (1988) Infect. Immun. 56:1120, used a monoclonal antibody to the N. meningitidis serogroup C (xe2x80x9cMenCxe2x80x9d) capsular polysaccharide to elicit an anti-idiotype antibody. Mice immunized with the anti-idiotype antibody were protected against infection with a lethal dose of MenC bacteria. These experimenters subsequently demonstrated that a peptide fragment of a MenC anti-idiotype antibody elicited serum anti-MenC antibodies and protected animals from bacteremia and death after lethal challenge with MenC bacteria. Westerink et al. (1995) Proc. Natl. Acad. Sci. USA 92:4021.
However, to date, no such approach has been taken with respect to MenB vaccine development. It is readily apparent that the production of a safe and effective vaccine against MenB would be particularly desirable.
The present invention is based on the discovery of functionally active antibodies directed against MenB PS derivatives, wherein the antibodies do not cross-react, or are minimally cross-reactive, with host tissues as determined using the assays described herein. These antibodies therefore pose minimal risk of evoking autoimmune disease and are termed xe2x80x9cnon-autoreactivexe2x80x9d herein. Assays used herein to determine autoreactivity include binding assays against a neuroblastoma cell line expressing long chain polysialic acid residues on the cell surface. Specifically, antibodies that are negative in these assays are considered to lack autoreactivity. The non-autoreactive antibodies are particularly useful for identifying molecular mimetics of unique MenB PS epitopes that can be used in vaccine compositions. Furthermore, the antibodies, humanized versions of the antibodies, fragments and functional equivalents thereof, will also find use in passive immunization against, and/or as an adjunct to therapy for, MenB and E. coli K1 disease. Since such molecules do not bind to polysialic acid in host tissue as determined by the autoreactivity assays described herein, they provide a safe and efficacious method for the treatment and/or prevention of MenB and E. coli K1 disease.
Accordingly, in one embodiment, the subject invention relates to antibodies directed against MenB PS derivatives, wherein the antibodies are not autoreactive with host tissue. Such antibodies may further be characterized as being capable of eliciting functional activity against MenB bacteria. One particular group of such antibodies is also characterized as non cross-reactive with Neisseria meningitidis serogroup B capsular polysaccharide (NAc-MenB PS) in an ELISA. However, these antibodies are anti-capsular in that they can bind to the cell surface of a Group B encapsulated bacteria, but not to capsular-deficient mutants.
Another embodiment of the invention relates to monoclonal antibodies directed against MenB PS derivatives, and hybridomas producing those monoclonal antibodies.
Other embodiments of the invention relate to unique Neisseria meningitidis serogroup B epitopes that are capable of being bound by the antibody molecules of the present invention.
Still further embodiments of the subject invention are related to methods for isolating molecular mimetics of unique epitopes of MenB PS and molecular mimetics identified using the methods. The methods comprise:
(a) providing a population of molecules including a putative molecular mimetic of a unique epitope of MenB PS;
(b) contacting the population of molecules with the antibodies described above under conditions that allow immunological binding between the antibody and the molecular mimetic, if present, to provide a complex; and
(c) separating the complexes from non-bound molecules.
In another embodiment, the subject invention is directed to a vaccine composition comprising a unique epitope of MenB in combination with a pharmaceutically acceptable excipient.
In yet another embodiment, the invention is directed to a vaccine composition comprising a molecular mimetic of a unique epitope of MenB in combination with a pharmaceutically acceptable excipient.
In still a further embodiment, the invention is directed to a vaccine composition comprising an anti-idiotypic antibody molecular mimetic of a unique epitope of MenB in combination with a pharmaceutically acceptable excipient.
In yet further embodiments, the invention relates to pharmaceutical compositions comprising the antibodies described above.
In another embodiment, the subject invention is directed to a method for treating or preventing MenB and/or E. coli K1 disease in a mammalian subject comprising administering an effective amount of the above pharmaceutical compositions to the subject.
These and other embodiments of the present invention will readily occur to those of ordinary skill in the art in view of the disclosure herein.